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US Astronomers Surprised Formation of Big Galaxies Continues


U.S. astronomers have discovered massive new galaxies evolving in our corner of the universe. This means that galaxy-forming processes thought to have ended eons ago continue relatively nearby, making it easier to study how these massive congregations of stars come about.

Until now, astronomers thought that the birth rate of the universe had declined dramatically and that only small galaxies were forming. But a satellite launched by the U.S. space agency NASA 16 months ago has witnessed the birth of huge baby galaxies not far from us.

Johns Hopkins University astronomer Tim Heckman says the busiest days of major galaxy formation ended about 10 billion years ago, but the Galaxy Evolution Explorer spacecraft (GALEX) has shown that it continues at a reduced rate.

"It changes our picture of how galaxies like our own Milky Way may have formed," he said. "It looks like some galaxies like this may still be forming today, which is quite remarkable. These galaxies give us a great opportunity to study the processes that gave birth to galaxies in an up close and personal way. It is almost like looking out the window and seeing a dinosaur walking by."

Mr. Heckman and colleagues saw nearly 40 bright, compact galaxies that greatly resemble the youthful galaxies of more than 10 billion years ago, when our Milky Way is believed to have formed. These infant galaxies are only two to four billion light years away and may range in age from just 100 million to one billion years. The youngest have not had time to develop the spiral shape of the Milky Way and many other mature galaxies.

They shine brightest in the ultraviolet wavelengths invisible to our eyes. This is because they have not had time to form many bright stars and would appear very dim through an optical telescope. Bright ultraviolet emissions are typical of violent star-forming regions and exploding old stars called supernovae, which supply the gas for new stars.

Tim Heckman says the U.S. GALEX satellite, which surveyed thousands of galaxies before finding these few, sees them easily with its ultraviolet telescope.

"They look like bright blue blobs," he added.

Now that scientists know the new galaxies are out there, they will train other ultraviolet telescopes on them to study them in detail. Astronomer Alice Shapley of the University of California at Berkeley says they offer the first close-up view of what the Milky Way and many other galaxies looked like in their infancy.

"The GALEX sample is so close by that we can obtain exquisitely detailed information from it about all the processes that are involved in galaxy formation," she said. "So, thus, I think we will be able to answer detailed questions about galaxy formation that are impossible to address with distant galaxies in the early universe."

The new findings will be published in a forthcoming issue of Astrophysical Journal Letters.

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